Higher River Flows Benefit Wild Trout
In response to a forecast for much-below-average temperatures, the Island Park Reservoir Drought Management Committee met on December 3 and agreed to increase reservoir outflow to 300 cubic feet per second (cfs) from the 90 cfs that had been released throughout most of October and November.
Flows were raised immediately after the meeting and only hours before an extended period of sub-zero weather settled into eastern Idaho. Because trout cannot regulate their body temperature, the ability of young trout to avoid predators is very limited when water temperatures drop. Their survival depends on availability of spaces among rocks and wood along the banks where they can conceal themselves from predators. Downstream of Island Park Dam, the number of these hiding spaces is directly related to water flow.
The 300 cfs outflow is far greater than had been anticipated earlier in the summer, but conservative water management and timely precipitation throughout the late summer and early autumn resulted in fill of the reservoir to 50% of capacity by early December, allowing the higher outflow. The Committee, which includes HFF, Fremont-Madison Irrigation District, U.S. Bureau of Reclamation, Idaho Department of Fish and Game and others, will meet regularly throughout the winter and adjust flows as necessary in response to weather, reservoir fill rate, and snowpack. The Committee's objectives for the winter are to attain near-average content in the reservoir by April 1, maximize flows during critical periods for juvenile trout survival, and allow the Island Park hydroelectric plant to operate for the remainder of the winter.
|The photo above shows the Buffalo River fish ladder after only four days of sub-zero temperatures.|